Carat Weight refers to the weight of a diamond. The carat is often confused with the size even if it is actually a unit of weight.
A carat can also be divided into 100 "points". A diamond of 0.75 carats can also be referred to as a diamond of 75 points or ¾ of a carat.

A one-carat diamond does not cost exactly twice as much as a half-carat diamond, as larger diamonds are rarer in nature, which places them at the top of the diamond quality pyramid, a one-carat diamond will cost much more than double that of a half carat diamond of the same color, clarity and cut.

The carat of gold

When approaching gold jewelry, the first distinction to be made concerns the carat of the metal, i.e. the amount of pure gold present in the alloy that makes up the jewel.

The term carat, that is the unit of purity with which gold is evaluated, derives dall’arabo qīrā (part twenty-fourth). Consequently, pure gold is commonly referred to as 24 karat gold, as it is composed of all 24 parts that make up a unit of gold or, expressed in thousandths, 999 gold.

24K gold, however, turns out to be too ductile for the composition of a jewel; for this reason, 999 other metals are added to gold, including copper, palladium and silver.

In Italy, in fact, most of the jewels on the market are offered in 18K gold in which pure gold constitutes 18 of the 24 parts of the alloy (if expressed in thousandths, 750 gold as it constitutes 75%).

In other markets, the gold carat of which the jewels are made may be different; in the United Arab Emirates, for example, 22 K gold is mainly traded, in the United States, Germany, England and France, 14 karat gold (585 gold) is widespread and in economically developing countries it is purchased mainly 9-karat gold (375 gold).